Highly resilient polypropylene yarn

ABSTRACT

Textured Polypropylene yarn possessing high resilience comparable to nylon as a result of unique structural configuration. The yarns are particularly suited for use in carpeting and upholstery.

United States Patent Miller et al. 145 A 29, 1972 [54] HIGHLY RESILIENT 5 R f ren Cit d POLYPROPYLENE Y N UNITED STATES PATENTS 72 I t Robert m w 3,296,681 1/1967 'Lopatin ..264/168 1 men J. Cm $12,: an: 3,262,257 7/1966 Martin ..2s/72.12 cohjmbia both ofsc 3,315,014 4/1967 Coover, Jr. et al. ..8/DlG. 9 3,363,041 1/1968 Shickman e161. ..264/168 [73] n N QF f Primary Examiner-Robert F. Burnett I Assistant Examiner-Raymond O. Linker, Jr. 2 Attomey-Thpmas A. Beck 21 A 1. 6.= 31,362 [57] ABSTRACT v Textured Polypropylene yarn possessing high 'lience com arable to n lon as a result of uni ue s2 U.S. c1. 7 P Y q 151: C. ..f...':?,:-2;1;1133::;11ss 73;" m 58 Field ofSearch ..16l/173; 264/168; 57114011;

HIGHLY RESILIENT POLYPROPYLENE YARN The present invention relates to highly resilient textured polypropylene yarns which are 'narticularly useful in carpeting and upholstery. V

Except for its poor resiliency, polypropylene is an ideal fiber to be used in carpeting and upholstering. Resiliency is a measure of the ability of a fiber to recover fully its original dimensions upon release of a stress which is compressing it. In the case of polypropylene carpet the poor resiliency is demonstrated by the walking out of a sculptured carpet in highly trafficked areas or by the matting which occurs on the walked on areas of level pile carpets. The matting phenomenon also occurs in upholstery which contains polypropylene pile yarn.

The present invention provides a highly resilient textured polypropylene yarn which has been formed, textured and heat treated in such a way as to have specific characteristics. The total of these characteristics results in a marked improvement in the resiliency and performance of the polypropylene yarns which possesses properties comparable to textured nylon yarns. The yarns of the present invention show an improved resiliency (as compared to a standard polypropylene yarn) while maintaining the additional properties necessary to result in a commercially acceptable high quality carpet or upholstery. 3

It is believed that the novel yarns of the present invention have a unique molecular and crystalline internal structural configuration which result in the physical characteristics described as follows: i

l. The fibers which comprise the yarn have a three dimensional crimp. Crimp is a term used to describe the waviness of a fiber and is a measure of the difference between the length of the unstraightened and that of the straightened fibers. Crimp can be produced in most fibers using texturing processes. The crimps induced in the fibers of the present invention have an arcuate configuration in three axes (such as in an S) as opposed to fibers possessing a sharp angular con-figuration (such as in a Z) which are not included within the scope of the present invention. The effect of the three dimensional crimp results is that the filaments in the yarns do not lean in one direction on compression of the pile.

2. The crimp in the fibers comprising the yarn is random in nature so that it will not nest together and lean in unison when the pile is compressed.

3. The yarn has an average crimp count range of 6 to crimps per inch, preferably 9 to 15 crimps per inch.

4. At least 75 percent of the crimp in the yarn has the rounded arcuate convolutions described above; however, the fibers comprising said yarn are nonhelical along their length. The sharp edge (Z) angular configuration in the crimp as produced by a stuffer box assembly is unsatisfactory since this form leads to weak spots on repeated compression. Helically crirnped yarn is unacceptable because it tends to nest and become entangled on compression, thereby minimizing recovery of the yarn when used in carpet pile or upholstery.

5. Greater than 80 percent of the filaments which comprise the yarn exhibit substantially no plastic deformation (as determined by microscopic examination). Plastic deformations are weakened areas resulting from centralized stress in the fiber along its length at the angles of intersection of the angular (Z) type fiber. The plastic deformations result in loss of resiliency in the yarn upon repeated compression. In contrast the fibers possessing a rounded (S) configuration as in the present invention exhibit better stress distribution on compression.

6. The textured tenacity of the yarn of the present invention must be 'less than 2.5 grams per denier with a preferred range of 0.8 to 2.25 grams per denier. This tenacity is obtained by drawing the fiber at a ratio of 3.0:1 or less. The lower tenacity yarn is used because it leads to high resiliency and minimizes the tendency for fibrillation.

7. The average crimp permanence of the yarn is 20 to with a preferred range of 30 to 60.

The crimp permanence value noted above provides a measure of means for evaluating on an arbitrary scale, several factors inherent in the yarns of the present invention. These factors are: t

A. The number of crystallites which are formed in the shape of the crimp or texture due to a heat treating step after texturing. In the texturing step i the fibers contain crystallites in a straight form which are mechanically distorted during texturing. The heat treatment forms the crystallites in the shape of the crimp. A high crimp permanence value indicates a large number of crystallites in the texture shape.

B. The storage life of the yarn texture for bulk continuous filament polypropylene on pims or packages shows some tendency to lose some of its texture on storage possibly due to creep or plastic flow. The texture of the yarn of the present invention has a markedly improved storage life. The yarn having higher crimp permanence has the best storage characteristics.

C. Yarn having low crimp permanence figures (less than 20) tend to bulk less. In carpet or tufted upholstery after dyeing or scouring this lower level of bulk results in elongated tufts. The elongated tuft bends at its base on compression. The base is a weak point upon repeated compressions which results in the tufts flattening and taking on the appearance of fish scales. In contrast, yarns with high crimp permanence afford good bulk and a pulleddown tuft which is mechanically sounder and better able to support weight and recover readily, much as would be expected from a series of leaf springs. This type of texture compresses without being forced over on its side.

The following is a description of the method used to determine the percent Crimp Permanence.

i. Individual samples of the yarns listed in Table 1 approximately 16-18 inches long are separately tied to form a loop. If the yarn sample contains twist, this must be untwisted to the point of 0.25 turns/inch or less before being tied. The loop of yarn is then hung in an air oven at C. 1*: 2 C. with a weight (0.15 gldenier) suspended from the loop.

ii. After 15 minutes the yarn sample is removed from the oven and allowed to cool for 15 minutes without tension.

% Crimp permanence= Original length-bulked length (length after steaming) X100 The following table lists the percent Crimp Permanence for various commercial yarns as determined using the above noted procedure.

TABLE 1 Crimp Permanence Herculon (Hercules Inc.) 9.0 Polycrest (SDR-ZS Uniroyal Inc.) 12.7 Polycrest (SDR-1 Uniroyal Inc.) 13.0 Textured Polypropylene yarn of present invention 30-50 Chemstrand Nylon 2600 den. 32.0 Allied Nylon 2600 den. 29.I duPont SOl Nylon 50.4

8. The yarn exhibits some elastomeric character at low elongations. This is demonstrated by drawing the yarn on an Instron tester to percent elongation. Comparison of the tenacity at 8 percent elongation on the first outgoing cycle and return cycle indicate at least a 40 percent above average modulus retention. (In this case the yarn sample is initially tensioned sufficiently to just remove the texture). The elastomeric property noted aids the resiliency of the yarn because the hysteresis for energy lost on compression or bending of the fiber is reduced. (Bending of a filament results in elongation on one side and compression on the other).

The polypropylene which is used in the present invention may be any of the commercially available essentially linear highly crystalline isotactic polypropylenes which have a high molecular weight and a melting point of about 165 C. The polypropylene used in the present invention is generally prepared using a coordination polymerization method. This polymerization method uses a reduced transition metal catalyst, generally in the form of a slurry of a very small solid particle in an inert medium. This method is well known in the art.

Various additives including such dye receptors as polyamines, polyvinylpyridines, polyamides, organic pigments such as phthalocyanine etc., inorganic pigments such as. the cadmium salt series, carbon black, etc., and stabilizers, plasticizers, flame retardants etc. may be incorporated into the polypropylene to modify the properties thereof.

The conversion of the bulk polypropylene to fiber form is accomplished by any of the usual spinning methods. Since polypropylene can be melted under reasonable temperature conditions, the production of the fiber is preferably done by melt spinning as opposed to solution processes.

In the process of melt spinning, the polymer is heated in an extruder to the melting point and the molten polymer is pumped at a constant rate under high pressure through a spinnerette containing a number of holes. The liquid polymer streams emerge downward from the face of the spinnerette usually into a cooling stream of gas, generally air. The streams of molten polymer are solidified as a result of cooling to form filaments and are brought together and are wound up on bobbins. If desirable the polymer melt in the extruder may be protected from oxygen by blanketing it with steam or an inert gas such as carbon dioxide, nitrogen, etc.

After the fiber has been prepared a drawing step is usually performed to orient the molecular structure of the fibers. The drawing step may be carried out in any convenient manner using techniques well known in the art such as the use of a heated pin, a heated plate, heated liquids, cool liquids, or the like. The methods are not critical but the draw ratio (i.e., drawn length/undrawn length) should be kept below about 3.0: l. The fibers are combined to form yarns which are then textured to impart a crimp therein. Any texturing means which imparts a three-dimensional non helical, curvilinear rounded configuration to the yarn can be used to prepare the yarns of the present invention. Generally, a stream of compressible fluid such as air, steam, or any other compressible fluid or vapor capable of exercising a plasticizing action on the yarn is vigorously jetted from a nozzle through a portion of the yarn as it continuously travels through the texturing device, at a temperature about 200 F.

The temperature of the fluid must be such that the yarn does not melt. If the temperature of the yarn is above the melting point of the yarn it is necessary to shorten the time in which the yarn dwells in the texturing region.

There are a number of methods and devices for producing a turbulent stream of fluid for the purpose of texturing yarns. Suitable methods and devices are described in US. Pat. No. 3,363,041 and copending application, Ser. No. 31,206 filed Apr. 23, 1970, by Robert J. Clarkson entitled Yam Rebound Texturing Apparatus and Method, the contents of which are hereby incorporated by reference herein, although the invention is not limited to these methods or devices.

After a crimp is imposed in the yarn as described above the yarn is taken from the texturing region with a minimum of tension in the highly compacted state and is post-heated in suitable means at temperatures from about 250 F. to just below the softening point of the fiber for a sufficient period of time to allow the crimp imparted during the texturing step to be permanently set into the fiber. For some applications desirable yarns are achieved by heat treating textured yarns in the range between 265 F. and 280 F. It has been determined experimentally that polypropylene yarns containing up to 10 percent poly( vinylpyridine) which were heated in an oven to heat treat the yarn, tended to lose the fine hand which it possesses at lower temperatures. Pigmented fiber similarly treated showed no noticeable loss of hand so the phenomenon associated with the modified polypropylene yarns at temperatures above about 295 F. may be due to sensitivity of the polyvinylpyridine additive to heat and oxidation When the crimp of the yarn has been permanently set the yarn is withdrawn from the post-heating zone allowed to cool and is wound up under slight tension on pims.

The post-heating treatment can be performed on a continuous basis whereby the yarn travels through a heated tube or chamber, or the post-heat treatment can be done using a batch method whereby the yarn is fed directly from the texturizer into a heated container. Hot air, steam or any other heated medium can be used as the heat source in the continuous or batch methods after post heating.

The yarn may be twisted after texturizing and heating treating if desired. There is no limitation on the cross sectional shape, denier per filament or total denier of the fibers which comprise the yarn. Some crunodal loops are apparent in the yarn but these do not affect the invention.

The following examples serve to illustrate the invention.

EXAMPLE I Four skeins of yarn from crystalline polypropylene of melt index 5 (Profax made by the Hercules Polymer Company of Wilmington, Delaware) containing respectively (a) 2.91 percent poly(vinylpyridine) as a dye additive (b) cadmium, (c) phthalocyanine, or (d) carbon black pigment (solution dyed) as well as heat stabilizers, antioxidants, U.V. stabilizers are prepared by extruding the compositions through a 52 round hole spinnerette (hole size 0.030 inch) to afford four 2,100 denier yarns. Melt index of the yarns is about 7.5. These yarns are drawn :1, 2 plied and then texturized using the apparatus and techniques described in Example 2 of copending Ser. No. 31,206, filed Apr. 23, 1970 entitled Yarn Rebound Texturing Apparatus and Method. The yarns are then cooled to near room temperature, pulled out and wound onto a package. Each yarn is now a 2,600 denier carpet yarn. Tenacity of this yarn is about 1.7 g/den. with an elongation of 70 percent. An examination of the yarns prepared using this method discloses that all four possess the characteristics which place them within the scope of the present invention as set forth below.

TEST RESULTS The four yarns possess a 3-dimensional random crimp; an average of l 1 crimps per inch; at least 90 percent of said crimp possesses rounded convolutions and nonhelical along the length; in each yarn greater than about 90 percent of the filaments comprising same possess substantially no plastic deformation along their lengths; the tenacity of the yarns averaged about 1.7; the average crimp permanence value is 38; and the yarns all possess a modulus retention of at least 40 per cent at 8 percent elongation.

EXAMPLE 2 The procedure of Example 1 is duplicated to prepare modified dyeable polypropylene and pigmented polypropylene yarns with the exception that the yarns (drawn 2.521) are textured using the procedure described in U.S. Pat. No. 3,441,989. The yarns are heated by means of circulating air at a temperature of 270 F. for about 15 minutes through a can which contains said yarns.

Upon examination it is found that each yarn possesses values and characteristics similar to the values and characteristics of the yarns set forth in the test results in Example 1, so the yarns prepared in the manner described also fall within the scope of the present invention.

EXAMPLE 3 Three level loop carpets were tufted and mock dyed. These consisted of carpeting sold under the trademark Polycrest which contains 156 filaments comprising polypropylene and about 3 percent poly(vinylpyridine); 501 Nylon (highest resiliency nylon commercially available), and the high resiliency polypropylene containing the poly(vinylpyridine) dye additive and prepared as described in Example 1 herein to possess 4,000 denier. These carpets were then subjected to mechanical pounding at 1,380 cycles/hour, each cycle being a pressure of 7 PSI over a 1-% of an inch diameter area. Thickness of the pile is measured initially then after 1,000, 3,000, 10,000 and 20,000 cycles. The pile thickness is measured with a dial gauge with a 1 inch diameter foot. The pressure applied while taking the measurement is 0.75 PS1. The results are presented in Table 2.

TABLE 2 Initial Pile Cycles of Pounding Hf. Wt.0z./ Rating in Matting Carpet (lnches) Sq.Yd. 1000 3000 10,000 20,000 Polycrest (SDR-25-4000 den.) .245" 30 9.0 12.6 18.4 19.6 501 Nylon (4000 den.) .253" 30 5.1 6.7 8.3 10.7 High Resiliency Polyprop. 4000 denier .231" 30.8 5.2 6.5 9.9 12.1

%Matting=hi-h/hiX 100 h pile height (less backing) after matting test (inches) hi initial pile height (less backing) Table 2 shows that the yarns of the present invention compare favorably with nylon.

EXAMPLE 4 Equal weight carpets (approximately 25 oz.) of 156 filament (4,000 denier) polypropylene yarn containing 3 percent poly(vinylpyridine) were tufted into a sculptured pattern maintaining stitches/inch and pile height as close as possible. These samples were all dyed to the same color, latexed, and put into highly trafficked areas. The number of people walking through this area were counted by photocounter. These carpets were graded subjectively at intervals during the test for matting and pattern deformation.

TABLE 3 Tenacity Matting and Pat- Crimp (g/den.) of tern Deformation Perm- Textured Draw Rating Sample anence Yarn Ratio 8,000 16,000 24,000 A 13.0 3.1 40:! 5-D D-E E B 14.0 2.5 3.0:1 S S-D D C 12.7 1.9 2.5:1 S S S-D D 13.5 1.4 2.021 N N-S S as described in Example 1 including a heat treatment to 7 8 msmrm What we claim and desire to protect by Letters Box) 9.0 2.0 2.5:1 S-D D-E E Patent F 38.0 1.8 2.5:1 N N N-S l. A highly resilient yarn comprising crystalline polypropylene filaments characterized by:

5 A. A three dimensional crimp;

B. Said crimp being random in nature;

' C. 6 to crimps per inch;

D. At least 75 percent of said crimp having rounded convolutions with said filaments being non-helical 0 along their length;

E. Greater than 80 percent of said filaments comprising said yarn possessing substantially no plastic deformation along their lengths;

F. A tenacity less than 2.5 grams/denier;

G. A crimp permanence of 30-60;

H. Possesses a modulus retention of at least 40 percent at 8 percent elongation.

2. The yarn defined in claim 1 wherein the filaments possess an average crimp count of 9-15 crimps per 20 inch.

3. The yarn defined in claim 2 wherein the tenacity is "N None S Slight D Definite E Extreme Samples A, B, C, and D show the change in resiliency as a function of tenacity alone. The samples were textured using the method described in Example 1, but were not heat treated after texturing to permanently set the crimp. These samples have the crimp characteristics required in the present invention (three dimensional shape, etc.), except for Crimp Permanence and elasticity. Sample E lacks the crimp characteristics as well. Although the tenacity of Sample E is low (equivalent to Sample C), the resiliency of Sample E is 15 lower due to it having been crimped in a stufler box so it possesses a two dimensional crimp containing sharp edges and plastic deformation. Sample F was prepared permanently set the crimp, and a 4,000 denier yarn was obtained. This yarn has all the requirements of the present invention and demonstrates the improved between and g Per f resiliency that can be expected. This example shows The yam defined clafm l 'Pf 9 to that no Single property or characteristic of 10 percent by weight poly(vrnylpyr1d1ne) in admixture polypropylene yarns is responsible for the unexpec- 25 Said Polypropylene tedly high resiliency yarns of the present invention. The The yam in f contains a yams of the present invention result from the tow minor amount of organic or inorganic pigment to color combination of essential properties and characteristics said assetforth herein. 

2. The yarn defined in claim 1 wherein the filaments possess an average crimp count of 9-15 crimps per inch.
 3. The yarn defined in claim 2 wherein the tenacity is between 0.80 and 2.25 grams per denier.
 4. The yarn defined in claim 1 which contains up to 10 percent by weight poly(vinylpyridine) in admixture with said polypropylene.
 5. The yarn defined in claim 1 which contains a minor amount of organic or inorganic pigment to color said yarn. 